Interference signal removing apparatus and rf receiver using the same

ABSTRACT

An interference signal removing apparatus of a radio frequency (RF) receiver includes a low noise amplification unit which performs low noise amplification, a feedback processing unit which removes a necessary signal in a desired band from a signal output from the low noise amplification unit, and performs feedback of the signal from which the necessary signal is removed, and a signal processing unit which transmits a processed RF signal by synthesizing an input RF signal and the feedback signal to the noise amplification unit.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit under 35 U.S.C. § 119(a) of a KoreanPatent Application No. 10-2008-0002177, filed on Jan. 8, 2008, in theKorean Intellectual Property Office, the disclosure of which isincorporated herein by reference in its entirety.

TECHNICAL FIELD

The following description relates to an interference signal removingapparatus and a radio frequency (RF) receiver using the same.

BACKGROUND

In an RF receiver, an RF filter is generally used between an antenna anda low noise amplifier (LNA). The RF filter performs a function of a bandpass filter (BPF) which passes signals of desired bands among a diverserange of channels, and filters signals of undesired bands. Such an RFfilter may be difficult to integrate into a single chip. Where the RFfilter is implemented on a chip, the performance of the RF filterdegrades, and accordingly, the RF filter is typically implemented usingan external element such as a surface acoustic wave (SAW) filter.

FIG. 1 illustrates an apparatus for removing interference signals in aconventional RF receiver. As illustrated in FIG. 1, the conventionalinterference signal removing apparatus includes an antenna 10, an RF SAWfilter 20, and a LNA 30. Where RF signals are transmitted to the antenna10 through a channel, the RF SAW filter 20 performs band pass filteringand the on-chip LNA 30 of the RF receiver suppresses noise and amplifiesdesired signals.

The RF SAW filter 20 is an external element and it is not integratedinto a single chip. It is also necessarily provided with an external SAWfilter for each desired band in order to selectively receive the desiredband among a multi-band, so the cost and size of the SAW filter mayincrease.

SUMMARY

In one general aspect, there is provided an apparatus for removinginterference signals by performing a feedback processing in an RFreceiver.

In another general aspect, an interference signal removing apparatusincludes a low noise amplification unit which performs low noiseamplification of an input RF signal, a feedback processing unit whichremoves a necessary signal in a desired band from a signal output fromthe low noise amplification unit and performs feedback of the signalfrom which the necessary signal has been removed, and a signalprocessing unit which transmits a processed RF signal by synthesizingthe input RF signal and the feedback signal to the low noiseamplification unit.

An interference signal may be removed from the processed RF signal bysynthesizing the input RF signal and the feedback signal.

The feedback processing unit may include a band reject filter.

The feedback processing unit may further include an amplifier whichamplifies the signal processed by the low noise amplification unit, andtransmits the amplified signal to the band reject filter.

The feedback processing unit may include an in-phase signal processingunit which removes a necessary signal from an in-phase signal of thelow-noise-amplified signal, a quadrature signal processing unit whichremoves a necessary signal from a quadrature signal of thelow-noise-amplified signal, and a signal mixing unit which mixes thesignals processed by the in-phase signal processing unit and thequadrature signal processing unit, and transmits the mixed signal to thesignal processing unit.

The in-phase signal processing unit and the quadrature signal processingunit each may include a down-mixing unit which lowers a frequency of thelow-noise-amplified signal to a baseband, a high-pass filter whichfilters out the necessary signal from the signal adjusted to thebaseband, and an up-mixing unit which raises a frequency of thehigh-pass-filtered signal to an RF band.

A local frequency used in the down-mixing unit may be the same as thatused in the up-mixing unit.

The apparatus may further include a second low noise amplification unitwhich is connected to an input port of the interference signal removingapparatus.

In still another general aspect, a radio frequency (RF) receiverincludes a low noise amplification unit which performs low noiseamplification of an input RF signal, a feedback processing unit whichremoves a necessary signal in a desired band from a signal output fromthe low noise amplification unit, and performs feedback of the signalfrom which the necessary signal has been removed, and a signalprocessing unit which transmits a processed RF signal by synthesizingthe input RF signal and the feedback signal to the noise amplificationunit, wherein the low noise amplification unit, the feedback processingunit, and the signal processing unit are integrated into a single chip.

An interference signal may be removed from the processed RF signal bysynthesizing the input RF signal and the feedback signal.

The radio frequency (RF) receiver may further include an antenna toreceive an RF signal of a multi-band.

Other features will become apparent to those skilled in the art from thefollowing detailed description, which, taken in conjunction with theattached drawings, discloses exemplary embodiments of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating an exemplary interference signalremoving apparatus of a conventional RF receiver.

FIG. 2 is a block diagram illustrating an exemplary interference signalremoving apparatus of a RF receiver according to an exemplary embodiment

FIG. 3 is a diagram illustrating an exemplary interference signalremoving apparatus of FIG. 2 in more detail.

FIGS. 4A to 4E are diagrams illustrating exemplary waveforms of a signalat each node of an interference signal removing apparatus according toan exemplary embodiment.

FIG. 5 is a diagram illustrating an exemplary interference signalremoving apparatus of a RF receiver according to another exemplaryembodiment

FIGS. 6 and 7 are diagrams illustrating exemplary interference signalremoving apparatuses of RF receivers according to yet another exemplaryembodiments.

Throughout the drawings and the detailed description, the same drawingreference numerals will be understood to refer to the same elements,features, and structures.

DETAILED DESCRIPTION

The following detailed description is provided to assist the reader ingaining a comprehensive understanding of the methods, apparatuses and/orsystems described herein. Accordingly, various changes, modifications,and equivalents of the systems, apparatuses and/or methods describedherein will be suggested to those of ordinary skill in the art. Also,description of well-known functions and constructions are omitted toincrease clarity and conciseness.

FIG. 2 illustrates an exemplary interference signal removing apparatus100 of an RF receiver 200 according to an exemplary embodiment. Asillustrated in FIG. 2, the RF receiver 200 includes an antenna 110 andthe interference signal removing apparatus 100. The interference signalremoving apparatus 100 includes a low noise amplification unit 120, afeedback processing unit 130, and a signal processing unit 140. The lownoise amplification unit 120 receives an RF signal through the antenna110 and performs low noise amplification. The feedback processing unit130 removes a necessary signal of a desired band from a signal outputfrom the low noise amplification unit 120, and performs feedback. Thesignal processing unit 140 provides the low noise amplification unit 120with a processed RF signal from which an interference signal is removedby synthesizing the RF signal input and the feedback signal.

FIG. 3 illustrates the interference signal removing apparatus 100 of theRF receiver 200 of FIG. 2 in more detail, and FIGS. 4A to 4E illustratewaveforms of a signal at each node of the interference signal removingapparatus. Hereinafter, the operation of the interference signalremoving apparatus 100 of the RF receiver 200 is described withreference to FIG. 3 and FIGS. 4A to 4E.

An RF signal of a multi-band is input through the antenna 110. As shownin FIG. 4A, at node A, the RF signal shows a waveform of multi-bandsignals having different center frequencies f₁, f₂, f_(c), f₃, and f₄.For example, a signal of a band having the center frequency of f_(c) isa necessary signal of a desired band, and the other signals areunnecessary signals which operate as interference signals. Forconvenience of description, it is assumed that the gains of differentmulti-band signals are identical as 1.

At node B, the input RF signal is amplified to have a gain of A₀ by thelow noise amplification unit 120, and the low noise amplification unit120 may be implemented as a low noise amplifier (LNA). In the signalpassing through the low noise amplification unit 120, noise components,such as thermal noise, which are received with the input RF signal maybe reduced.

A necessary signal is removed from the signal processed by the low noiseamplification unit 120 by a band reject filter 150 of the feedbackprocessing unit 130. Since the bandwidth of signals transmitted from atransmitter (not shown) is known, a user may select a bandwidth toremove necessary signals using the band reject filter 150. At node D,the signal passing through the band reject filter 150 has onlyunnecessary signals as shown in FIG. 4D, since a necessary signal havingthe center frequency of f_(c) has been removed.

The feedback processing unit 130 may further include an amplifier 160 inaddition to the band reject filter 150. The amplifier 160 may bedisposed in front of or behind the band reject filter 150. The amplifier160 may be a low noise amplifier or a general amplifier having afunction of lowering noise. At node B, the signal processed by the lownoise amplification unit 120 is fed back to the feedback processing unit130, and passes through the amplifier 160. The band reject filter 150removes the signal having the center frequency of f_(c) from theamplified signal, so only unnecessary signals remain.

The signal processing unit 140 synthesizes the signal passing throughthe band reject filter 150 (D node) and the signal input through theantenna 110, so that the unnecessary signals are removed and thenecessary signal remains (E node). According to an aspect, the synthesisindicates synthesis of the signal input through the antenna 110 and thesignal output from the feedback processing unit 130 having a phasedifference of substantially 180° from the input signal. According toanother aspect, the signal from which the unnecessary signals, that is,interference signals, are removed, is input again to the low noiseamplification unit 120, and is repeatedly fed back to the feedbackprocessing unit 130 until the gain of the unnecessary signals becomes 0,that is, until the unnecessary signals are removed.

In order for the signal processing unit 140 to remove the unnecessarysignals, the signal (D node) passing through the band reject filter 150of the feedback processing unit 130 should have a phase difference ofsubstantially 180° from the input RF signal. An element such as asubtractor which generates a phase difference of 180° may be used toobtain the signal remaining after the necessary signals have beenremoved (D signal) from the input RF signals (A node). Alternatively, aninverting amplifier may be used, or the gain of the amplifier 160 may bedesigned to have a negative value, so that a phase difference of 180° isachieved.

As shown in FIG. 3, the signal from which the necessary signal has beenremoved (D node) may be input to an output port (B node) of the lownoise amplification unit 120. Where the signal processing unit 140 islocated at the output port of the low noise amplification unit 120, thesignal passing through the low noise amplification unit 120 and thesignal from which the necessary signal has been removed may besynthesized. In this case, since the unnecessary signals are removed atthe output port of the low noise amplification unit 120, linearcharacteristics are lower than where the unnecessary signals are removedat an input port of the low noise amplification unit 120 as shown inFIG. 3.

As described above with reference to FIGS. 3 and 4A to 4E, theinterference signal removing apparatus 100 of the RF receiver 200receives RF signals of only a desired band, so a plurality of SAWfilters are not necessarily required for filtering outside the chipwhere multi-band RF signals are received. Accordingly, costs formanufacturing the interference signal removing apparatus of the RFreceiver and the size of the interference signal removing apparatus maybe reduced.

FIG. 5 illustrates an exemplary interference signal removing apparatus105 of an RF receiver 210 according to another exemplary embodiment. Theinterference signal removing apparatus 105 of FIG. 5 further includes alow noise amplification unit 170 between the antenna 110 and the signalprocessing unit 140 in addition to the configuration of FIG. 3, andshows an example of the band reject filter 150.

As shown in FIG. 5, the interference signal removing apparatus 105 ofthe RF receiver 210 further includes the low noise amplification unit170 which performs low noise amplification of an input RF signal.Accordingly, the signal processing unit 140 removes unnecessary signalsby synthesizing the low-noise-amplified RF signal and a signal processedby the feedback processing unit 130. Since the low noise amplificationunit 170 is formed between the antenna 110 and the signal processingunit 140, interference signals generated during the feedback process ofthe feedback processing unit 130 is removed. Accordingly, theinterference signal removing apparatus 210 of the RF receiver 210 mayhave more enhanced noise preventing features.

Further shown in FIG. 5, the band reject filter 150 of the feedbackprocessing unit 130 may be implemented as a circuit in which an inductorL is serially connected to a capacitor C. As shown in FIG. 5, one portof the inductor L of the serial LC circuit is connected to a nodebetween the signal processing unit 140 and the amplifier 160, and oneport of the capacitor C is grounded. Accordingly, the serial LC circuitoperates as a band reject filter, so a necessary signal is removed bythe earthed port and unnecessary signals are transmitted to the signalprocessing unit 140.

FIG. 6 illustrates an exemplary interference signal removing apparatus680 of an RF receiver 600 according to yet another exemplary embodiment.The interference signal removing apparatus 680 of the RF receiver 600 ofFIG. 6 includes a low noise amplification unit 620 and a signalprocessing unit 670 which are the same as that of the interferencesignal removing apparatus 100 of the RF receiver 200 of FIG. 3.Accordingly, descriptions thereof are omitted herein.

A feedback processing unit 660 includes an in-phase signal processingunit 690, a quadrature signal processing unit 695, and a signalsynthesis unit 675. The in-phase signal processing unit 690 removes anecessary signal from an in-phase signal of a low-noise-amplifiedsignal. The quadrature signal processing unit 695 removes a necessarysignal from a quadrature signal of the low-noise-amplified signal. Thesignal synthesis unit 675 synthesizes the signals processed by thein-phase signal processing unit 690 and the quadrature signal processingunit 695, and outputs the synthesized signal to the signal processingunit 670.

The in-phase signal processing unit 690 and the quadrature signalprocessing unit 695 may each include down-mixing units 630 and 635,high-pass filters 640 and 645, and up-mixing units 650 and 655. Thedown-mixing unit 630 or 635 lowers the frequency of thelow-noise-amplified signal to a baseband. The high-pass filter 640 or645 filters out necessary signals from among the signal adjusted to thebaseband. The up-mixing unit 650 or 655 raises the frequency of thefiltered signal to the RF band.

Hereinafter, the operation of the feedback processing unit 660 whichremoves a necessary signal using a single sideband modulation mannergenerally used in a communication field is described.

The down-mixing units 630 and 635 each multiply a signal passing throughthe low noise amplification unit 620 by local frequencies f_(IL) andf_(QL) of an in-phase component and a quadrature component,respectively, so that the frequency band of the signal is transited to abaseband. A phase difference of substantially 90° is generated betweenthe in-phase component and the quadrature component similarly to thesine and cosine functions.

In the baseband, the high-pass filters 640 and 645 perform high-passfiltering of the signals, so that necessary signals are removed. Thehigh-pass filters may be implemented as capacitors, first and secondfilters, or the like.

The up-mixing units 650 and 655 each multiply the signal from which thenecessary signal has been removed by local frequencies f_(IH) andf_(QH), respectively, so that the frequency band of the signal istransited to the RF band.

The signals output from the in-phase signal processing unit 690 and thequadrature signal processing unit 695 are synthesized by the signalsynthesis unit 675, and transmitted to the signal processing unit 670.The description of the signal processing unit 670 is omitted here toavoid repetition.

The frequency in the down-mixing units 630 and 635 may be the same asthat in the up-mixing units 650 and 655 so as to perform filteringwithout errors. According to an aspect, high-pass filtering is performedin the baseband instead of in the RF band so that more precise removalof the necessary signal may be implemented.

FIG. 7 illustrates an exemplary interference signal removing apparatus685 of an RF receiver 605 according to yet another exemplary embodiment.The RF receiver 605 of FIG. 7 further includes a second low noiseamplification unit 625 which is formed at an input port of the RFreceiver 600, that is, between the antenna 610 and the signal processingunit 670. The second low noise amplification unit 625 may be the same asthat of the interference signal removing apparatus 105 of the RFreceiver 210 of FIG. 5. Accordingly, detailed description of the secondlow noise amplification unit 625 is omitted here to avoid repetition.Moreover, the interference signal removing apparatus 685 includes thelow noise amplification unit 620, the signal processing unit 670, andthe feedback processing unit 660 which are the same as that of theinterference signal removing apparatus 680 of the RF receiver 600 ofFIG. 6. Accordingly, descriptions thereof are omitted herein.

It is understood that the terminology used herein, for example, a lownoise amplification unit, may be different in other applications or whendescribed by another one skilled in the art. As an illustration, a lownoise amplification unit disclosed herein may be described or taught asa noise amplification unit which performs low noise amplification.

A number of exemplary embodiments have been described above.Nevertheless, it will be understood that various modifications may bemade. For example, suitable results may be achieved if the describedtechniques are performed in a different order and/or if components in adescribed system, architecture, device, or circuit are combined in adifferent manner and/or replaced or supplemented by other components ortheir equivalents. Accordingly, other implementations are within thescope of the following claims.

1. An interference signal removing apparatus comprising: a low noiseamplification unit which performs low noise amplification; a feedbackprocessing unit which removes a necessary signal in a desired band froma signal output from the low noise amplification unit, and performsfeedback of the signal from which the necessary signal is removed; and asignal processing unit which transmits a processed radio frequency (RF)signal by synthesizing an input RF signal and the feedback signal to thenoise amplification unit.
 2. The apparatus of claim 1, wherein thefeedback processing unit comprises a band reject filter.
 3. Theapparatus of claim 2, wherein the feedback processing unit furthercomprises an amplifier which amplifies the signal processed by the lownoise amplification unit, and transmits the amplified signal to the bandreject filter.
 4. The apparatus of claim 2, wherein the feedbackprocessing unit comprises: an in-phase signal processing unit whichremoves a necessary signal from an in-phase signal of thelow-noise-amplified signal; a quadrature signal processing unit whichremoves a necessary signal from a quadrature signal of thelow-noise-amplified signal; and a signal mixing unit which mixes thesignals processed by the in-phase signal processing unit and thequadrature signal processing unit, and transmits the mixed signal to thesignal processing unit.
 5. The apparatus of claim 4, wherein thein-phase signal processing unit and the quadrature signal processingunit each comprise: a down-mixing unit which lowers a frequency of thelow-noise-amplified signal to a baseband; a high-pass filter whichfilters out the necessary signal from the signal adjusted to thebaseband; and an up-mixing unit which raises a frequency of thehigh-pass-filtered signal to an RF band.
 6. The apparatus of claim 5,wherein a local frequency used in the down-mixing unit is the same asthat used in the up-mixing unit.
 7. The apparatus of claim 1, furthercomprising a second low noise amplification unit which is connected toan input port of the interference signal removing apparatus.
 8. Theapparatus of claim 1, wherein the signal processing unit transmits theprocessed RF signal from which interference signals are removed bysynthesizing the input RF signal and the feedback signal to the noiseamplification unit.
 9. A radio frequency (RF) receiver comprising: a lownoise amplification unit which performs low noise amplification; afeedback processing unit which removes a necessary signal in a desiredband from a signal output from the low noise amplification unit, andperforms feedback of the signal from which the necessary signal isremoved; and a signal processing unit which transmits a processed RFsignal by synthesizing an input RF signal and the feedback signal to thenoise amplification unit, wherein the low noise amplification unit, thefeedback processing unit, and the signal processing unit are integratedinto a single chip.
 10. The RF receiver of claim 9, further comprisingan antenna to receive the input RF signal.